1. Field of the Invention
This application relates to tubulars, for example, tubulars used in transporting fluids, in drilling, completion and/or production of oil and gas wells, or in injecting and/or producing gas, brine and/or water. This invention also relates to methods and apparatuses to hold to tubulars.
2. Brief Description of the Related Art
Tubular strings may be used, for example, to transport fluids and to produce water, oil and/or gas from geologic formations through earthen bores. In geologic applications, a drilled bore may be cased with a string of tubulars (e.g., a casing) to prevent collapse of the bore and to facilitate deeper drilling. In casing operations, a number of devices are generally coupled to a tubular. For example, devices that may be coupled to a tubular may include bore wall scrapers and wipers, packers, centralizers and landing collars. Devices may be coupled to a tubular, either at a fixed position or within a range of positions, using holding devices called stop collars.
Stop collars may be used to limit or prevent movement of a device coupled on the exterior of a tubular. A device may be coupled to a tubular in a floating mode (e.g., axially and radially slidable) intermediate two axially-spaced stop collars secured to the tubular. For example, a bow-spring centralizer may be movable along a tubular, but limited from further axial movement by the end collars of the centralizer being disposed between two stop collars (or intermediate a stop collar and a non-flush tubular connection). This configuration is called a straddling configuration, and permits the centralizer to “float” or move along the exterior of the tubular within a range defined by the axial separation of the stop collars (or by the axial separation of a stop collar and a non-flush tubular connection).
A bow-spring centralizer may be coupled to a tubular in a floating mode using a stop collar secured to the tubular between the two end collars of a bow-spring centralizer, e.g., within the span of the bow-springs. This configuration facilitates pulling the bow-spring centralizer through restrictions during the running of the tubular into a bore.
In another application, stop collar may be used to position an expandable packing member on a tubular to form a packer. In one packer embodiment, stop collars may serve a dual purpose. First, the stop collars may each comprise a packer face disposed to straddle the packing member and thereby limit or prevent axial expansion of the packing member. Second, the stop collars may prevent a pressure differential applied across the expanded packing member from moving the packing member relative to the tubular. Pressure differentials may be applied across a packing member in, for example, cementing, perforating, fracture isolation and other downhole operations.
FIG. 1A is schematic of a packer 110 comprising an expandable packing member 160 received on a tubular 8 between straddling stop collars 132 and 134. The tubular 8 and packer 110 are illustrated as being run into a bore 7 of a larger tubular (e.g., casing) 88. Depicted stop collars 132 and 134 each comprise packer faces 132A and 134A, respectively, that engage ends of the packing member 160 to restrict movement of the packing member 160 during running of the tubular into the bore 7. The packing member 160 may comprise a material that swells upon contact by an activating fluid (not shown) to an expanded mode, for example as illustrated in FIG. 1B, to isolate an annulus first portion 7A from an annulus second portion 7B.
After expansion of a packing member 160′, e.g., in the configuration illustrated in FIG. 1B, the packer faces 132A and 134A may stabilize the packing member 160′ of FIG. 1B against being moved by a pressure differential between the annulus first portion 7A and the annulus second portion 7B. The packer faces 132A and 132B may be disposed at an angle to an axis of the bore of the tubular 8, which angle may be perpendicular as illustrated in FIG. 1B or any other angle desired.
Instead of a swellable packing material, a packer may comprise an inflatable packing member. The tubular and the attached packer may be run into a bore and the packing member may be inflated using a source of pressurized fluid. As with the swellable packing member, the packer faces may also restrict the axial expansion of an inflatable packing member and thereby force the packer to radially expand upon inflation of the packing member to engage the bore 7, which may be the bore of a larger tubular, such as casing, or the bore of an uncased earthen hole.
In low-clearance applications, the thickness of a stop collar is an important design parameter because a stop collar adds to the positive outer diameter (P.O.D.) of the tubular and may determine whether the tubular to which the stop collar is coupled will pass a bore restriction. Restrictions may be presented by, for example, the diameter of the bore of a tubular larger than the tubular to which the stop collar is secured (e.g., casing), a blow-out preventer (BOP), valve, liner or a bore irregularity. As a result, a low-clearance stop collar may be essential to certain downhole operations.
Load capacity may also an important design factor relating to stop collars, especially for low-clearance stop collars. A stop collar may be required to bear potentially large forces imparted to the stop collar while moving the tubular through the tightest passable restrictions. The tubular string may weigh hundreds of tons, and forces imparted to a stop collar, for example, due to impact with a restriction, may exceed about 45 kN (10,116 pounds).
As another example of how loads may be imposed on a stop collar, a low-clearance, bow-spring centralizer may be coupled to a tubular using a low-clearance stop collar secured to the tubular between the end collars of the bow-spring centralizer. The bow-spring centralizer may pass through bore restrictions that require flexible collapse the bow-springs to lie substantially flat along the exterior of the tubular on which the centralizer is coupled. A low-clearance stop collar secured to the tubular between the end collars of the centralizer will not substantially impair collapse of the bow-springs. The reactive force provided by the stop collar to pull the leading end collar of the centralizer through such a restriction will be at least equal to the force imparted by the restriction on the bow-springs of the centralizer as they collapse to lie along the exterior of the tubular.
Conventional stop collars may be too large in outer diameter for certain applications. Additionally, conventional stop collars may not provide sufficient holding force without damaging the tubular. A conventional stop collar may be coupled to a tubular using, for example, a set screw. For example, a set screw comprising a shaft threadably received in an aperture machined in a collar. The shaft is rotatable to threadably advance radially inwardly to engage and bite into the exterior of the tubular. Set screw-type stop collars rely on highly localized contact with the tubular and typically do not provide adequate load capacity on tubulars of hardened materials, such as high-carbon steel or other extremely hard alloys, because the set screw does not sufficiently penetrate the surface of the hardened tubular. Even a set screw-type stop collar having multiple set screws “bites” into only a small cumulative area on the tubular, and the load capacity is limited, especially on hardened tubulars.
When the load capacity of a set screw-type stop collar is exceeded, the set screws may slip and cause scratching and scoring of the tubular, thereby damaging any protective coatings and/or possibly creating corrosion initiation sites.
Other conventional stop collars may be crimped onto a tubular. FIG. 2 is schematic of a prior art expandable packer (packing member 165 in the retracted mode) mounted on a mandrel having internally threaded connections 124 at the ends for connection between adjacent tubular segments of a tubular string. The collars 125 and 129 may include set screws 99 to position the collars on the tubular 8 to be crimped, by application of radially inward forces, to grip the tubular 8 and prevent movement of the packing member 162 along the mandrel 123. In the crimping process, the collars 125 and 129 are deformed to engage the tubular 8.
A shortcoming of crimped stop collars is that they generally require deformation of the wall of the tubular 8 (or the mandrel) on which the stop collar is installed in order to provide sufficient load capacity, and deformation of the tubular (or the mandrel) may be impractical or undesirable. Also, crimping a collar onto a tubular may require a heavy machine to generate the forces required to deform the collar and/or the tubular, and this requirement may prohibit field installation. A shortcoming of a sub-mounted packer (see FIG. 2) is that the packer must be positioned at a threaded connection within a tubular string, and it cannot be conveniently disposed at any location along any tubular segment.
Another type of stop collar comprises an adhesively-secured pad of epoxy adhesive and/or plastic resin material disposed in a pre-activated condition on the exterior of a tubular using, for example, the method disclosed in U.S. Pat. No. 7,195,730 to Calderoni, et al. The epoxy adheres to the tubular and resists movement once the epoxy or plastic resin cures. Adhesively-secured stop collars, like set-screw type stop collars, may lack sufficient load capacity required to, for example, push or pull a centralizer through a tight restriction. Adhesively-secured stop collars may also require careful surface preparations such as, for example, cleaning, degreasing, brushing and/or sand blasting, to ensure that the adhesive will adhere to the tubular. Adhesively-secured stop collars may also require a period of inactivity after application for the adhesive to cure enough for the stop collar to bear a load. Other stop collars may comprise a plastic compound or resin molded onto the tubular. A stop collar comprising a plastic compound molded onto the tubular may chip or shatter from impact with bore restrictions, and a piece of the stop collar may break off and become lodged in a critical piece of equipment, such as a BOP or valve, or it may otherwise impair movement of the tubular within a the bore.
What is needed is a stop collar for securing a device on a tubular that can be installed at a field location, such as a pipe yard or on a rig. What is needed is a stop collar that can be installed at any position along the length of a tubular. What is needed is a stop collar that is compatible with low-clearance applications. What is needed is a stop collar that provides a sufficient load capacity. What is needed is a stop collar that is compatible for use on expandable tubulars. What is needed is a stop collar that can reliably secure a device to premium grade or hardened tubulars. What is needed is a stop collar that minimizes or eliminates marking, scarring and scoring of the tubular on which it is secured. What is needed is a stop collar that can be secured to a tubular without the need for heavy machines, without highly skilled personnel, and without the need for time-consuming surface preparation. What is needed is a stop collar that can be secured on a tubular in any climate.